Casing structure for electrical appliances



P.- K. CRAMBLET CASING STRUCTURE FOR ELECTRICAL APPLIANCES May 12, 1931.'

Filed March` 5, 1930 released May 12, 1931 STATES PAUL K.

LET, (JF ELKHART, INDIANA., ASSIGNOR, BY MESNE ASSIGNMENTS, T0

MOLIS-HONEYWELL REGULATOR COMPANY, 0F MINNEAPOLIS, MINNESOTA,

A COEPQRATION 0F DELAWARE CASING STRUCTURE FOR ELECTRICAL APPLIANCES Application led March 5, 1930. Serial No. 483,812.

My invention relatesin general to electrical appliances of the type includin hermeticall sealed vitreous containers o glass or the like and more particularly to a mer- J,cury switch of the type having an outer envelope of metal loaded glass such as lead glass. i

ln manufacturing mercury switches of this type the outer envelope or lead glass casing E@ has a tubulation fused or sealed thereto and electrodes sealed therein. Itis desirableto use a lead glass casin because of its capacity to effectively and ermetically seal around the leading-in wire, which are commonly copj@ per clad or Dumet wire. The outer casing is completely closed except for the tubulation and the tubulation a'ords the means for introducing mercury into theswitch, for exhausting the air therefrom and ror filling ga' the switch with an atmosphere of inert arc suppressing gas, usually hydrogen. Following these operations the tubulation is 4sealed oh' to complete the sealing of the switch. The' sealed oft portion ci the tubulation is as known as the sealing tip of the switch.

With mercury switches of this type, that is, of the type having a metal loaded glass casinguor lead glass casing it has always been the practice to form the tubulation of the same material as the casing. Thus, with a lead glass case the practice has always been to fuse a lead glass tubulation to the case and, of course, to form the sealing ti by fusing and twisting the lead glass tubu ation in the nal step of the manufacture of the switch Sealing tips so formed have always been lrnown to present a Zone of weakness in the casing or outer envelope of the switch and not infrequently these sealing tips crack or split open especially when subjected to unusual strains vas when operated with an extreme snap action or subjected to severe j olts while the mercury in the tube is in or fills the sealing tip or when the mercury is thrown Vforcibly-into the sealing tip. The usual line of cleavage is on a plane in which the axis of the sealing tip lies.

l have vdiscovered that the cause of the 5G weakness of the sealing tips of metal loaded 55 lead loaded glass this core 1s, of course, constituted of minute articles of free metallic lead. rlhis reduction of the metal results from the high heat to which the tubulation is subjected to form the sealing tip and to the presence of hydrogen not only in the flame but e@ also in the switch since the switch has been :filled with hydrogen. Thus, the main p0rtion of the sealing tip is formed of lead loaded glass with the lead chemically combined in the glass composition while the core is formed of a glass of diEerent structure or character, to-wit: a glass impregnated with nely divided but free metallic lead particles. Such a sealin tip structure is inherently Weak and suscepti le to crackling or fracture, rst for the reason that the core with its tree lead possesses a different co-eiicient of expansion from that or the lead-loaded portion of the sealing tip immediately surrounding the same, second, because the lead core reduces materially the cohesion of the sealing tip structure', and finally for the reason that the interior ofthe sealing tip so constituted presents a sharply tapered or wedge-like forma- 80 tion peculiarly susceptible to splitting when the mercury in the switch is forcibly thrown thereinto. lt follows that a sealing tip so constituted is not well adapted to withstand mechanical strains or temperature changes and frequently the cohesion of the structure is so poor that va slight leakage path occurs ythrough the sealing tip. rIhis latter deciency is extremely undesirable as it permits air to leak into the switch and to impair the inert and arc suppressing properties of the atmosphere within the sw1tch.

To remedy these disadvantages while retaining the advantages of the lead loaded casing, l propose to utilize a tubulation of e5 glass that is free of metal Vbut which has a coeihcient of expansion suciently close to that of the lead glass to permit of readily and effective fusing or unitin of the tabulation and the casing. Prefiere 1y the tubulation is le@ constituted of lime glass which readily fuses to a lead glass casing, but which, of course, will not be weakened during the formation of the sealing tip because of the absence of any metalin the lime glass that might be reduced and form a core. On the contrary, the lime glass tubulation, when sealed off to form the sealing tip, presents a homogeneous and cohesive structure effectively united to the lead glass case and 'capable of withstanding mechanical strains and temperature variations enlarged scale; and

without liability of fracture or cracking and Within danger of leakage. p

Other objects and advantages reside in certain novel features of the construction, arrangement and combination of parts which will be hereinafter more fully described and particularly pointed out in the appended switch as constructed after the tubulation has been fused thereto but before the tubulation has been sealed olf to form a sealing tip;

Figure 3 is a fragmentary sectional view showing the structure of the sealing tip on an Figure 4 is a view similar to Figure 3 but showing the structure of the ordinary lead glass sealing tip.

Referring to the drawings, and more particularly to Figure 1, the numeral l designates an outer envelope or casing of lead glass. At one end of the casing a pinch seal 2 is provided about leading-in wires 3 and 4, the wires 3 and 4 being welded at their inner ends to electrodes 5 and 6 with which a body of mercury 7 is cooperable to make and break the electric circuit in which the switch is incorporated. At the end of the casing or envelope opposite the pinch seal. a sealing tip 8 is providedA and is formed of lime glass or other glass free of metal.

In constructing the switch shown in Figure l, a tubulation T of lime glass is first fused or united as at 10 to one end of the case 1, the case l being melted down to unite with the tubulation as shown in Figure 2. After the mercury has been introduced through the tubulation, the switch evacuated or exhausted in its air and the h drogen atmosphere supplied thereto, the tu ulation T is melted down to form the sealing tip 8 which is free of metal and of uniform or homogeneous structure and composition so that all of its portions have the same co-efiicient of expansion and so that the cohesive properties of the lime glass are not impaired. Further, the interior of the sealing tip has the rounded formation shown in Figure 3 with the advantage that should the mercury 7"be thrown into the tubulation it will not tend to wedge or force the walls thereupon.

This advantage can be better appreciated by a comparison of Figure 3 with Figure 4. Figure 4 shows the structure of the conventional lead glass ealing tip which has its interior sharply tapered or of wedge formation so that if mercury is thrown violently thereinto it will-tend to pry the walls apart. The wedge formation of the prior sealing tips results from t-he reduction of the lead which prevents the glass on the inside of the tip from flowing in to the desirable rounded formation. Further, the sealing tip of the present invention as shown in Figure 3 is free of the metallic core of finally divided and free metal which is indicated by the stippling in Figure 4 and which, as explained a'bove, impairs the cohesion of the glass as well as its capacity to withstand temperature variations or mechanical strains. And along with with these advantages in the sealing tip, there is the capacity in the'lead case structure to effectively and hermetically seal with the leading-in wires.

It is to be understood that the type or structure of the mercury switch may be Varied and that the tubulation may be connected or fused to the casing or outer envelope at any desired point or location.

I claim:

1. A mercury switch comprising an outer envelope of lead glass, electrodes sealed therein, a body of mercury in the envelope cooperable with the electrodes, and a sealing.;r tip constituted of lime glass and fused to the lead glass of the outer case.

2. A mercury switch comprising an outer envelope of metal loaded glass, electrodes and mercury sealed therein, and a sealing tip of met-al free glass and having approximately the same co-eiicient of expansion as the glass of the case and fused to the case.

3. In a device of the character described, an evacuated container of metal loaded glass and a sealing tip Vof metal free glass having approximately the same co-eiicient of eX- pansion as the metal loaded glass and fused thereto.

4. In a device of the character described,

an hermetically sealed lead glass case, and av lime glass sealing tip fused thereto.

In witness whereof, I ax my signature.

PAUL K. CRAMBLET.

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